1. Field of the Invention
The present invention relates to a drive arrangement for a rotary-type shredder, and more particularly to a hydraulic drive with a hydraulic pressure-actuated electrical reversing control.
2. Description of the Prior Art
Most rotary shredding devices of the type disclosed are driven directly by an electric motor through an appropriate speed-reducing transmission as shown, for example, in U.S. Pat. No. 3,845,907.
Although such electric drive motors may be provided with overload protection or a reversing circuit, as shown in such prior patent, they nevertheless tend to burn out when subjected to sudden excessive torque demands, such as when the cutters are jammed with material too hard or large for them to handle. Because of this deficiency in direct electric drives for such rotary shredders, they have also been driven with hydraulic motors using electric motor-driven hydraulic pumps to supply pressure fluid to such hydraulic motors. In this way the hydraulic motor circuit can be designed with relief valves to prevent excessive operating pressures and in this way isolate the electric pump motor from excessive torque loads. Such hydraulic motor circuits have also been designed with hydraulic reversing controls to automatically reverse the hydraulic motor when the shredder approaches a jamming condition to prevent such a condition. However, such hydraulic reversing controls have been unsatisfactory in that they are inconsistent and unreliable in their operation because of the effects of the varying temperature, viscosity and flow rate of the hydraulic fluid in the motor circuit.
Accordingly there is a need for a hydraulic drive for rotary shredders to prevent the burning out of electric motors and furthermore a hydraulic drive arrangement with a reliable and automatic reversing control to reverse the cutters and thereby prevent their jamming without the need for deactivating the shredder or its drive.